Gasification of sulphite thick liquor

Abstract

Method for recovering chemicals and energy from sulphite thick liquor containing organic and inorganic compounds obtained when producing pulp by chemical delignification of fibrous raw material using a sulphite pulping process, the method including processing of the organic and inorganic compounds at a global temperature above 800° C. whereby producing partly at least one phase of a liquid material and partly at least one phase of a gaseous material. The processing is carried out by gasification of the sulphite thick liquor in a gasification reactor at sub-stoichiometric conditions and in the presence of an oxidizing medium. The reactor has an opening in its bottom in the form of a chute which opens directly into a quench compartment.

1 . Method for recovering chemicals and energy from sulphite thick liquor, said sulphite thick liquor being obtained when producing pulp by chemical delignification of fibrous raw material using a sulphite pulping process, said sulphite thick liquor comprising organic and inorganic compounds; the method comprising:
 processing said organic and inorganic compounds at a global temperature above 800° C. ad producing partly at least one phase of a liquid material and partly at least one phase of a gaseous material; said processing is carried out by gasification of said sulphite thick liquor in a gasification reactor at sub-stoichiometric conditions and in the presence of an oxidizing medium, wherein said reactor having an opening in its bottom in the form of a chute, which opens directly into a quench compartment, said chute has a horizontal cross sectional diameter which is less than 40% of the largest cross sectional diameter in a horizontal plane of said reactor.   
     
     
         2 . Method according to  claim 1 , wherein said chute has a horizontal cross sectional diameter which is preferably being 5-35% of the largest cross sectional diameter in a horizontal plane of said reactor. 
     
     
         3 . Method according to  claim 1 , wherein said global temperature is at least 900° C., preferably at least 950° C. and below 1300° C. 
     
     
         4 . Method according to  claim 1 , wherein said gasification is an entrained flow gasification. 
     
     
         5 . Method according to  claim 1 , wherein the absolute pressure of the gasification process is about 1.5 to about 150 bar, preferably about 10 to about 80 bar, and most preferably from about 24 to about 40 bar in the reaction zone. 
     
     
         6 . Method according to  claim 1 , further comprising introducing said oxidizing medium to an inlet of the reactor in vicinity of an inlet of the reactor for introduction of sulphite thick liquor so that the oxidizing medium can be used for atomization of the sulphite thick liquor. 
     
     
         7 . Method according to  claim 1 , wherein said oxidizing medium is oxygen gas or an oxygen containing gas. 
     
     
         8 . Method according to  claim 1 , wherein said sulphite thick liquor forming droplets when meeting said oxidizing medium, said droplets having an average droplet size below 300 μm. 
     
     
         9 . Method according to  claim 7 , further comprising using steam as an atomization support medium by introduction of steam to the reactor through a separate inlet or by mixing said steam with said oxidizing medium before said oxidizing medium is introduced into the reactor through an inlet. 
     
     
         10 . Method according to  claim 1 , wherein said liquid material is in the form a salt melt, which is dissolved in a liquor thereby forming green liquor, said green liquor being drawn off from said reactor and being further processed in order to convert sodium sulphide comprised in the green liquor to sulphur dioxide and/or sulphite. 
     
     
         11 . Method according to  claim 10 , wherein said sodium sulphide is converted first to hydrogen sulphide by contacting said sodium sulphide in countercurrent with carbon dioxide and sulphur dioxide, preferably in an absorption/desorption tower, and then further to sulphur dioxide and/or sulphite. 
     
     
         12 . Method according to  claims 1 , further comprising obtaining a green liquor having an amount of unburnt charcoal in said green liquor lower than 5%, preferably lower than 1% and more preferred lower than 0.2%, of the carbon in the sulfite thick liquor. 
     
     
         13 . Method according to  claim 10 , further comprising obtaining a green liquor where sulphur found in said green liquor is to an extent of at least 90%, preferably at least 95% and more preferred at least 98%, in reduced form as sulphide. 
     
     
         14 . Method according to  claim 1 , wherein said resulting gaseous material is a raw synthesis gas comprising hydrogen sulphide, carbon monoxide, hydrogen and carbon dioxide. 
     
     
         15 . Method according to  claim 14 , wherein said hydrogen sulphide and said carbon dioxide in said raw synthesis gas are being removed from said raw synthesis gas in an acid gas removal plant thereby forming a hydrogen sulfide rich stream and a stream comprising mainly carbon dioxide from said acid gas removal plant. 
     
     
         16 . Method according to  claim 15 , wherein said resulting hydrogen sulfide rich stream comprises at least 25% hydrogen sulfide, preferably at least 35% hydrogen sulfide of its total stream content. 
     
     
         17 . Method according to  claim 15 , further comprising conveying the stream comprising mainly carbon dioxide from the acid gas removal plant to the recovery process. 
     
     
         18 . Method according to  claim 15 , wherein said hydrogen sulfide rich stream from said acid gas removal plant is being combusted directly with air or oxygen to give a combusted gas comprising sulphur dioxide, said sulphur dioxide being absorbed from said combusted gas in a gas scrubber. 
     
     
         19 . Method according to  claim 1 , wherein said sulphite thick liquor is a sodium based sulphite liquor or a potassium based sulphite thick liquor.